Chains are used in hoists to raise or lower payloads using wheels, pulleys or other actuators driven with an electric drive system. The chain of the hoist arrangement has to be inspected regularly in addition to full scale maintenance of the system. A worn out chain causes jamming of the drive and in worst case the worn out chain may break which may cause a serious accident. The chain can be inspected visually or by manual measurements but it takes a long time to inspect each link of the chain on a regular basis so its negative effect on productivity is substantial.
JP2013010634 discloses a lifetime judgement apparatus of a chain which comprises a rotation-detection unit which detects the rotation speed of arbitrary rotating shafts. The length of the chain is detected from pulses from the rotation-detection unit and compared to a predetermined length of a novel chain. A 5% elongation in the overall length of the chain is disclosed as a limit for alert.
One of the problems associated with the above arrangement is that the elongation in the overall length is not a good indicator of the condition of the chain. Hoists are not typically driven between their extreme points all the time so the chain does not wear evenly. The chain experiences most wear in the part which has the most interaction with the actuator moving the chain. One worn out link is enough to cause a malfunction or an accident even though all the remaining links would be intact. This kind of wearing would remain undetected if only elongation of the chain is measured.